scholarly journals Low-frequency variability in the Southern Ocean region in a simplified coupled model

2006 ◽  
Vol 111 (C5) ◽  
Author(s):  
Guillaume Maze ◽  
Fabio D'Andrea ◽  
Alain Colin de Verdière
Keyword(s):  
Southern Ocean ◽  
Low Frequency ◽  
Coupled Model ◽  
Low Frequency Variability ◽  
Ocean Region

scholarly journals Stochastic Subgrid-Scale Ocean Mixing: Impacts on Low-Frequency Variability

2017 ◽  
Vol 30 (13) ◽  
pp. 4997-5019 ◽  
Author(s):  
Stephan Juricke ◽  
Tim N. Palmer ◽  
Laure Zanna
Keyword(s):  
Southern Ocean ◽  
Interannual Variability ◽  
Time Scales ◽  
High Frequency ◽  
Low Frequency ◽  
Global Ocean ◽  
Small Scale ◽  
Subgrid Scale ◽  
Low Frequency Variability ◽  
Ocean Models

In global ocean models, the representation of small-scale, high-frequency processes considerably influences the large-scale oceanic circulation and its low-frequency variability. This study investigates the impact of stochastic perturbation schemes based on three different subgrid-scale parameterizations in multidecadal ocean-only simulations with the ocean model NEMO at 1° resolution. The three parameterizations are an enhanced vertical diffusion scheme for unstable stratification, the Gent–McWilliams (GM) scheme, and a turbulent kinetic energy mixing scheme, all commonly used in state-of-the-art ocean models. The focus here is on changes in interannual variability caused by the comparatively high-frequency stochastic perturbations with subseasonal decorrelation time scales. These perturbations lead to significant improvements in the representation of low-frequency variability in the ocean, with the stochastic GM scheme showing the strongest impact. Interannual variability of the Southern Ocean eddy and Eulerian streamfunctions is increased by an order of magnitude and by 20%, respectively. Interannual sea surface height variability is increased by about 20%–25% as well, especially in the Southern Ocean and in the Kuroshio region, consistent with a strong underestimation of interannual variability in the model when compared to reanalysis and altimetry observations. These results suggest that enhancing subgrid-scale variability in ocean models can improve model variability and potentially its response to forcing on much longer time scales, while also providing an estimate of model uncertainty.

scholarly journals The Low-Frequency Variability of the Southern Ocean Circulation

2013 ◽  
Vol 26 (16) ◽  
pp. 6081-6091 ◽  
Author(s):  
Emanuel Giarolla ◽  
Ricardo P. Matano
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
Average Rate ◽  
Bottom Topography ◽  
Low Frequency ◽  
Dominant Mode ◽  
Sea Surface ◽  
Wind Stress Curl ◽  
Low Frequency Variability ◽  
Long Time

Abstract Long time series of sea surface height (SSH), sea surface temperature, and wind stress curl are used to determine the main modes of low-frequency variability of the Southern Ocean (SO) circulation. The dominant mode is a trend of increasing SSH at an average rate of 3.3 mm yr−1. Similar trends have been reported in previous studies and the analysis indicates that the tendency of sea level increase over the SO has become more spatially homogeneous during the last decade, with changes in the increasing rate in 2000 and 2006. The other modes consist of stationary, basin-type modes, and an eastward-propagating wave. The stationary modes are particularly dominant in the Indian and Atlantic Ocean basins, where their spatial structure appears to be shaped by the basin geometry and the bottom topography. The wavelike patterns travel eastward with a period of approximately 10 years. Two waves were identified in the analysis: a complete cycle between 1997 and 2007 and a second cycle starting in 2000. Such waves have rarely been mentioned or identified in studies using recent satellite-derived SSH products.

scholarly journals Coupled Model Biases Breed Spurious Low‐Frequency Variability in the Tropical Pacific Ocean

2018 ◽  
Vol 45 (19) ◽  
Author(s):  
Dhrubajyoti Samanta ◽  
Kristopher B. Karnauskas ◽  
Nathalie F. Goodkin ◽  
Sloan Coats ◽  
Jason E. Smerdon ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Low Frequency ◽  
Coupled Model ◽  
Tropical Pacific ◽  
Tropical Pacific Ocean ◽  
Model Biases ◽  
Low Frequency Variability ◽  
The Tropical Pacific

Low frequency variability in an coupled ocean-sea ice general circulation model of the Southern Ocean

2013 ◽  
Vol 54 ◽  
pp. 200 ◽  
Author(s):  
Terence John O'Kane ◽  
Richard Matear ◽  
Matthew Chamberlain ◽  
James Risbey ◽  
Illia Horenko ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
General Circulation Model ◽  
General Circulation ◽  
Low Frequency ◽  
Circulation Model ◽  
Low Frequency Variability

scholarly journals Extratropical low-frequency variability with ENSO forcing: a reduced-order coupled model study  

2021 ◽  
Author(s):  
Stéphane Vannitsem ◽  
Jonathan Demaeyer ◽  
Michael Ghil
Keyword(s):  
Climate Models ◽  
Southern Oscillation ◽  
Low Frequency ◽  
Coupled Model ◽  
Ensemble Averaging ◽  
Reduced Order ◽  
Low Frequency Variability ◽  
Coupling Parameters ◽  
Parameter Ranges ◽  
The Impact

<p>The impact of the El Niño-Southern Oscillation (ENSO) on the extratropics is investigated in an idealized, reduced-order model that has a tropical and an extratropical module. Unidirectional forcing is used to mimic the atmospheric bridge between the tropics and the extratropics. The variability of the coupled ocean--atmosphere extratropical module is then investigated through the analysis of its pullback attractors (PBA). This analysis focuses on two ENSO-type forcings generated by the tropical module, one periodic and one aperiodic.</p><p> </p><p>For a substantial range of coupling parameters, multiple chaotic PBAs are found to coexist for the same set of parameter values. Different types of extratropical low-frequency variability are associated with each PBA over the parameter ranges explored. For periodic ENSO forcing, the coexisting PBAs are nonlinearly stable, while for the chaotic forcing, they are unstable and certain extratropical perturbations induce transitions between the PBAs. These distinct stability properties may have profound consequences for extratropical climate predictions, provided they are confirmed by studies using comprehensive climate models. Thus, for instance, ensemble averaging may no longer be a valid approach to isolate the low-frequency variability signal.</p>

scholarly journals DASSO: a data assimilation system for the Southern Ocean that utilizes both sea-ice concentration and thickness observations

2021 ◽  
pp. 1-6
Author(s):  
Hao Luo ◽  
Qinghua Yang ◽  
Longjiang Mu ◽  
Xiangshan Tian-Kunze ◽  
Lars Nerger ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Southern Ocean ◽  
Sea Ice ◽  
Coupled Model ◽  
Sea Ice Concentration ◽  
Model Free ◽  
Antarctic Sea Ice ◽  
Ice Concentration ◽  
Data Assimilation System ◽  
Assimilation System

Abstract To improve Antarctic sea-ice simulations and estimations, an ensemble-based Data Assimilation System for the Southern Ocean (DASSO) was developed based on a regional sea ice–ocean coupled model, which assimilates sea-ice thickness (SIT) together with sea-ice concentration (SIC) derived from satellites. To validate the performance of DASSO, experiments were conducted from 15 April to 14 October 2016. Generally, assimilating SIC and SIT can suppress the overestimation of sea ice in the model-free run. Besides considering uncertainties in the operational atmospheric forcing data, a covariance inflation procedure in data assimilation further improves the simulation of Antarctic sea ice, especially SIT. The results demonstrate the effectiveness of assimilating sea-ice observations in reconstructing the state of Antarctic sea ice, but also highlight the necessity of more reasonable error estimation for the background as well as the observation.

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